Craniosynostosis is a common birth defect that can occur as part of a syndrome or as an isolated anomaly. Though often defined as the premature closure of a cranial vault suture, anatomic and clinical studies reveal complex dysmorphology of the entire head. One complex trait typical of craniosynostosis syndromes is 'midfacial hypoplasia', a catch-all diagnosis that is defined on the basis of deficient development of the upper jaw, nasopharynx, and cheekbones presenting with a flatter than average face and associated respiratory difficulties. We have novel data from humans and mouse models of craniosynostosis which detail precise aspects of the cranial vault, cranial base, facial skeleton, facial sutures, and upper airway that are differentially affected by various FGFR2 and FGFR3 mutations. We hypothesize that the generalized condition of 'midfacial hypoplasia' represents a complex phenotype whose component parts differ depending upon the specific mutation. Relatively little is known about how the mutations identified as causative in craniosynostosis affect cells and tissues of the developing craniofacial complex to result in midfacial and choanal hypoplasia or atresia. In this project, we will perform quantitative analysis of 3D image data from human craniosynostosis phenotypes to formulate and test hypotheses pertaining to localized effects of various mutations in mouse models with craniosynostosis. We will use conditional mutant mice including Fgfr2+/S252W and Fgfr2+/P253R Apert syndrome, Fgfr2cC342Y/+ Crouzon/Pfeiffer syndrome, and Fgfr3+/P244R Muenke syndrome, and Wnt1-, Mesp1- and Sox17-2A-I-Cre-reporter mice to quantitatively study the differential effects of these mutations on specific craniofacial structures and cells and tissues that are derived from diverse embryonic tissues and that contribute to 'midfacial hypoplasia'. Once these precise phenotypic effects are defined on facial and cranial base phenotypes, we will analyze the role of these mutations on cell migration, differentiation, apoptosis, and proliferation. Finally, using RNA-seq, in situ hybridization, immunoblots, and immunohistochemistry on tissues micro-dissected from specific regions and developmental stages, we will scrutinize candidate Fgfr pathways (e.g., Erk1/2, p38) and identify novel pathways. We will provide essential information on dysmorphogenesis of the upper airway and face and establish objective criteria for the definition of midfacial and choanal hypoplasia needed to improve healthcare for numerous patients with these conditions.